Lecture 8: Combustion

Question 1

What is the combustion reaction in words

Answer 1

Fuel + Oxygen —–> Gases + Heat + Light

Question 2

What is the chemical combustion reaction

Answer 2

CH4 + 2O2 ——> 2H20 + Heat + Light

Question 3

What are the 3 sources of fuel for combustion

Answer 3

• Solid (woods)
• Liquids (accelerants)
• Gas (propane, butane etc.)

Question 4

What does heat do in a combustion reaction

Answer 4

Breaks the bonds of the reactants

Question 5

Why is combustion an exothermic reaction

Answer 5

Releases energy

Question 6

Why is combustion a continuous reaction

Answer 6

Combustion will continue until the fuel or oxygen runs out

Question 7

What are the factors affecting the rate of combustion

Answer 7

• Physical state of the fuel (solid, liquid or gas)
• The temperature of the flammable liquids

Question 8

• What are the different rates of a combustion reaction

Answer 8

• Detonation
• Deflagration

Question 9

• What is detonation

Answer 9

The speed of combustion is faster than the speed of sound (sonic), Produces a devastating shockwave which destroys everything

Question 10

*What is deflagration

Answer 10

The speed of the combustion reaction is slower than the speed of sound (subsonic), produces a wave of flame front.

Question 11

What are the combustible solids

Answer 11

• Pyrolyzable (Woods)
• Non-pyrolyzable (Charcoal, Cigarettes)

Question 12

What are pyrolyzable solids

Answer 12

Can undergo combustion at high temperatures, without the presence of oxygen.

Question 13

When wood undergoes pyrolysis what does it produce

Answer 13

gaseous products

Question 14

Gaseous products + Oxygen =

Answer 14

Flaming fire + heat

Question 15

How long does combustion of pyrolyzable solids last

Answer 15

Until all solids within the wood have been consumed

Question 16

What remains following the combustion of pyrolyzable solids

Answer 16

a carbon based residue which undergoes glowing combustion, smoldering

Question 17

What are non pyrolyzable solids

Answer 17

Undergoes glowing combustion

Question 18

What is charcoal

Answer 18

Pure carbon

Question 19

What happens when carbon is heated

Answer 19

Doesn’t break down or produce vapours, instead the surface oxidises and undergoes glowing combustion

Question 20

How does the oxidation of carbon occur

Answer 20

Oxidation starts at the outer surface, consumes it and moves onto the next surface and continues until there is nothing left.